The present invention relates to an NC machine tool, in particular, an NC machine tool capable of preventing a tool exchange error by the operator.
Conventionally, there have been NC machine tools having a function of automatically exchanging tools. For example, Japanese Laid-Open Patent Publication No. 11-33867 discloses a technique of detecting change of a machining program, tool exchange, change of data correction amount by sensors, in preparation for the case where the tool interferes with a machine, and decreasing rapid transverse speed of the tool to perform automatic operation of a machine tool. However, the technique serves to reduce damage caused by interference of the tool with the machine, not to prevent occurrence of a tool exchange error. For this reason, even when damage due to interference of the tool with the machine is suppressed, both of the tool and the machine can be damaged or operation of the machine tool can be stopped, resulting in a decrease in productivity.
Japanese Laid-Open Patent Publication No. 07-223148 proposes a technique of preventing an accident caused by a tool exchange error. According to the technique, at automatic operation of the NC machine tool, it is determined whether a correct tool is actually attached by detecting the shape of the attached tool by use of an optical sensor. However the technique has the disadvantage that it takes cost to construct a structure for recognizing the shape of the tool and determining the tool exchange error.